US2780435A

US2780435A - Turbine blade cooling structure

Info

Publication number: US2780435A
Application number: US330931A
Authority: US
Inventors: Jackson Thomas Woodrow
Original assignee: Individual
Current assignee: Individual
Priority date: 1953-01-12
Filing date: 1953-01-12
Publication date: 1957-02-05
Anticipated expiration: 1974-02-05

Description

Feb. 5, 1957 T. w. JACKSON 2,780,435

TURBINE BLADE COOLING STRUCTURE Fi1 ed Jam. 12, 1955 A lit mi! T hopuis WJ dlwom await/ax United States Patent ce 2,780,435 TURBINE BLADE COOLING STRUCTURE Thomas Woodrow Jackson, Cincinnati, Ohio, assignor to the United States of America as represented by the Secretary of the Navy Application January 12, 1953, Serial No. 330,931

Claims. (Cl. 25339.15)

(Granted under Title 35, U. S. Code (1952), see. 266) This invention relates to turbine blades and the like with particular reference to the cooling of the leading edges thereof In turbine blades subject to high gas-to-blade heat transfer with resultant corrosion and erosion of the blade metal, it becomes of considerable importance to provide effective means for cooling the leading edges. A cooling method heretofore used consists in attaching a displaced strip over the leading edge and passing air to the edge and strip through slots cut in the blade edge. A difficulty of this methodlies in the pronounced pressure reduction of the air flow due to the slot area, thus reducing the cooling effect on the strip to the danger point. To overcome this deficiency, fins are inserted in the slots but their use involves difficulty in manufacture. An added deficiency in the use of slots for cooling lies in the weakening elfect on the metal structure especially where it is necessary to use nonstrategic alloys.

A primary object of the present invention is to provide a blade cooling device which, while effectively cooling the blade edge, will not impart weakness to the blade structure. A further object is to insure adequate control over corrosion and erosion in turbine blades subject to high temperature gas flow. Still another object is to supply cooling arrangements such as will permit use of nonstrategic metals in turbine blade construction.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

Fig. 1 is a view of the improved blade in perspective with parts cut away to show the blade construction;

Fig. 2 is a detailed perspective view of the blade leading edge with the cap broken away to show the blade holes and lateral grooves; and

Fig. 3 is a sectional detail of the blade leading edge and cap plate.

Referring to Fig. 1 there is disclosed a turbine blade unit of the axial flow type consisting of the blade 11 and blade root 12. These two blade elements as here shown consist of a single integral member. The blade is hollow and is fashioned as an air foil with concaveconvex sides 5 and 6, a somewhat broadly rounded leading edge 8 and a sharpened trailing edge 9. The tip end 13 of the blade includes a plate 14 provided with an arcuate opening 15 therein extending over the greater portion of the tip area, the plate section 16 adjacent the leading edge being closed.

The blade root 12 is an extension of the blade and is formed in wedge shape with the blade integral with the blunt end 18 of the wedge and the side walls of the wedge formed with lateral ribs 19 to form a sliding engagement with correspondingly shaped receiving spaces in the turkbine hub.

Radially positioned in the hollow interior of the blade 2,780,435 Patented Feb. 5, V 1957 are a group of tubes 25 forming passages parallel to the longitudinal axis of the blade for carrying coolant therethrough and means for connecting said tubes to a source of coolant. The tubes which are shown in Fig. I extend from openings in the tip plate 14 to an arcuate opening or tube 26 in the root. This latter opening communicates through hub ducts to a source of air pressure. The purpose of the tubes 25 is to supply cooling air to the blade interior so that by cooling the tube walls the entire blade is cooled. The leading tube 25a (Fig. 3) is oversized to form a sealing barrier between the blade walls, thereby providing a closed forward chamber 27 in the blade.

Since the leading blade edge is subjected to highest heat effects, special cooling means are required to prevent excessive heat erosion and corrosion in this area. To this end the forward blade edge is perforated by a series of air ducts 30 which are alined radially with reference to the blade root and centrally or medially along the blade leading edge and which thus extend between the blade exterior and the interior forward chamber 27 of the blade; and the leading edge material laterally of each duct 30 and transversely of the blade edge is grooved, as best shownin Figs. 2 and 3, to form side channels 31 which serve .as guides to air flow for air moving outwardly through ducts 30.

Surmounting the leading edge and secured thereto centrally along the median line joining the ducts 30, is a blade-length U-shaped sessile cap 33, the skirts or walls 34 thereof being tapered in section to a thin edge 34a. This cap is fixed solidly to the leading edge, as by spot welding, at the raised points between the ducts 30, the side skirts or walls overlying the transverse channels 31 and a limited portion of the blade side walls 5 and 6 beyond these channel ends, thus forming lateral ducts from the :outlet ends of ducts 30. The curvature of the cap is lesser than that of the leading edge 8 so that with the cap attached in symmetrical relation to the blade, the cap skirts or walls diverge outwardly to form an increasing exit space for air passage from the outer openings of the ducts 30 to the cap edges. The channels 31 thus serve to provide direction reversing deflection of the air at the leading edge and to accelerate the air flow in the ducts 30, thereby to provide maximum cooling at the blade areas subjected to maximum heat. It is pointed out that the cap skirts 34, as shown in Fig. 1, are of uniform length along the blade and that the channels 31, as shown in Fig. 2, are of approximately equal length. Hence, the lateral ducts formed by the cap skirts and channels are of approximately equal length.

In operation, air from any appropriate pressure source is fed to the hub manifold (not shown) and thence to the blade root tube 26. From tube 26 the air flows to the tubes 25, the forward chamber 27 and ducts 30. The compressed air emitted from ducts 30 impinge on the cap 33 and is reversely turned through channels .31 to be discharged beyond the cap wall edges. The air reversal under pressure in contact with the cap rapidly withdraws heat from the cap and the cap in turn absorbs heat by conduction and radiation from the blade edge. Considerable convection cooling also takes place at the blade and cap surfaces. The tapered cap walls or skirts reduce the heat reservoir action thereof without affecting the air channelling action.

Obviously modifications and variations of the invention as disclosed are possible and it is to be understood therefore within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

blade -root* and'-' connectingisaid charnber to a sourceof coolant, a plurality-"ofoutwardly directed ducts formed througlrthe: leading edge: of said blade-andextending from said chamber tothe blade :exterior, a plurality of surface-grooves on .the leading edge=of said: blade extending transversely'fromv either side of the outer end of each' of said ducts -to fortncoolant channels, and an elongated sessile cap attached-t said 1 blade edge and overlying said: channels. to form transverse ducts, said cap having side" skirts forming: :1: direction reversing deflector for coolantflowing out of said outwardly extending duets? 2; Thebla'de coolingsd'evice. asdefinedv in claim 1, said blade having therein a pluralityof axially parallelipassageways con'nected to said bladeroot tube for carrying coolant through-said blade.

3; A cooling-device fortheleading edge of a turbine bladecomprising a-turbine blade having a leading edge, a sessile cap fixed along said leading edge having reversed side skirtsextendingover andspaced from the sides of said leading edge to form side spaces, a chamber within saidblade adjacent said-edge adaptedto receive coolant, a plurality of ducts alined centrally along said leading edge connecting said. chamber tothe outer edge surface inside said cap, and lateral ducts formed in the leading edge surface connecting said central ducts to the said spaces betweemsaid blade and cap side skirts, whereby coolant supplied said chamber will move through said ducts against said cap and in reverse direction along said cap skirts.

4. The cooling device for blade edges as defined in claim 3, said lateral ducts consisting of surface grooves of approximately equal length in the blade edge surface from the central duct outlets to apoint short of the trailing edge of said side.skirts on,..both sidesofsaid blade edge, whereby said lateral ducts are of approximately equal length.

5 A cooling device for blade edgescompris'inga bladelength leading blade edge of a givencurvature, abladelength reversely curved cap attachedv medially, along, said edge and having rearwardly directed skirts overlying and displaced from theside-surfaces of'said edge and forming a dischargev space .with said leadingedge and.apluraiity of radial ducts formed medially through said edge for supplying coolant to the rearward surface of said cap, said blade edge having lateral ducts connecting each of said radial ducts to the spaces between said, cap. side skirts and said bladeand said rearwardcap surface having a curvature lesser than that of'said blade edge, whereby the discharge space between cap and blade, increases progressively from forward to rearward.

References Cited in the file of this=patent UNITED STATES PATEI-ITS 2,220,420 Meyer Nov. 5,,1940. 2,236,426 Faber Mar. 25, 1941. 2,585,871 Stalker Feb. 12, 1952, 2,613,911 Clarke Oct. 14, 1952,